The Influence of the Correlated Colour Temperature (CCT) of LED Sources on the Protection of the Night Sky Against Light Pollution

Light pollution is a significant environmental issue that adversely affects ecosystem functioning, human health, and the quality of night sky observations. This paper investigates the influence of the correlated color temperature (CCT) of LED light sources on night sky brightness and the energy efficiency of outdoor lighting systems. The study included luminaires equipped with conventional discharge lamps, retrofit LED lamps with warm and cool correlated color temperatures, and an integrated LED luminaire. Laboratory measurements of luminous intensity distributions and spectral power distributions (SPDs) were performed, followed by numerical analyses using proprietary software developed in the Python 3.12 environment. The novelty of the proposed methodology lies in the application of the spectral metrics S/P, SSLR, and Acommon to assess the potential impact of light sources on night sky brightness. In addition, algorithms were developed to compare light sources based on their measured spectral power distributions rather than solely on manufacturer-declared parameters, such as correlated color temperature (CCT) or the color rendering index (Ra). The results show that LED light sources with higher correlated color temperatures emit a greater proportion of short-wavelength radiation, resulting in increased atmospheric scattering and a greater contribution to night sky brightness. The findings also demonstrate that an appropriate selection of the spectral characteristics of LED light sources can achieve a balance between energy efficiency and the mitigation of light pollution.